Block by fluoxetine of volume-regulated anion channels

Abstract

1. We have used the whole-cell patch clamp technique to study the effect of fluoxetine, a commonly used antidepressant drug, on the volume-regulated anion channel (VRAC) in calf pulmonary artery endothelial (CPAE) cells. We also examined its effects on other Cl- channels, i.e. the Ca2+-activated Cl- current (I(Cl,Ca)) and the cystic fibrosis transmembrane conductance regulator (CFTR) to assess the specificity of this compound for VRAC. 2. At pH 7.4 fluoxetine induced a fast and reversible block of the volume-sensitive chloride current (I(Cl,swell)), with a K(i) value of 6.0 ± 0.5 μM (n = 6-9). The blocking efficiency increased with increasing extracellular pH (K(i) = 0.32 ± 0.01 μM at pH 8.8, n = 3-9), indicating that the blockade is mediated by the uncharged form of fluoxetine. 3. Fluoxetine inhibited Ca2+-activated Cl- currents, I(Cl,Ca), activated by loading CPAE cells via the patch pipette with 1000 nM free Ca2+ (K(i) = 10.7 ± 1.6 μM at pH 7.4, n = 3-5). The CFTR channel, transiently transfected in CPAE cells, was also inhibited with a K(i) value of 26.9 ± 9.4 μM at pH 7.4 (n = 3) 4. This study describes for the first time the effects of fluoxetine on anion channels. Our data reveal a potent block of VRAC at fluoxetine concentrations close to plasma concentrations. The results suggest a hydrophobic interaction with high affinity between uncharged fluoxetine and volume-activated chloride channels. Ca2+-activated Cl- currents and CFTR are also blocked by fluoxetine, revealing a novel characteristic of the drug as a chloride channel modulator.